A considerable body of knowledge has developed on vinyl flooring materials and reinforcement materials for such flooring. Reinforcing layers, and more commonly, glass reinforcing layers, have received increasing attention in recent years for the construction of surface coverings. Floor coverings, in particular, have employed glass reinforcing layers, although the majority of the products which have contained such reinforcing layers have been developed in Europe. The reason for this appears to be that European dwellings are constructed primarily on concrete slabs which are dimensionally stable. In the United States, however, substantially different methods of construction are used in which most structures contain suspended wooden subfloors, including plywood and particleboard. Although structures of this type are less expensive than those containing concrete subflooring, suspended wooden subfloor is less stable than concrete when subjected to humid summer/dry winter seasonal changes.
Over the years, two systems have been developed for surface coverings which have come to be identified as self-induced tension floorings and loose-lay floorings. The present invention provides a new and useful surface covering which is capable of use either as a loose-lay surface covering or a tension surface covering. Because of its excellent accommodation, this surface covering can even be used over unstable substructures such as suspended wooden subfloors. A true hybrid surface covering is also disclosed which uses the characteristics of both loose-lay and tension flooring to permit use over suspended wooden subfloors.
Swart U.S. Pat. No. 2,800,423 entitled "Molded Article of Stretchable Glass Cloth" provided a concept of patterned cuts in a plastic sheet or glass cloth so that the sheet or cloth can be stretched and adapted for fitting compound curves without any need for cutting special patterns. There is no suggestion in Swart of placing the cloth in a pre-stressed condition or any advantage to use such a glass cloth over a substantially planar surface as the floors and other flat surfaces of the present invention.
Siddall U.S. Pat. No. 3,297,461 entitled "Reinforced Plastic Sheeting" disclosed how segmented inextensible filaments such as glass fibers encapsulated in polyvinyl chloride (PVC) can produce sheets capable of being stretched or compressed a small amount in any direction and any one portion of the sheet can be stretched or compressed without affecting any other portion so that the sheet could be used as flashing on a roof. Siddall teaches use of annealed metal filaments so that when deformed thay have no memory which tends to make them return to their original shape.
Evans U.S. Pat. No. 3,990,929, which is incorporated by reference, teaches methods of manufacturing and installing self-induced tension flooring or surface covering by manufacturing the structure on a thermally dimensionally stable backing. The backing not only serves as a carrier on which the flooring is manufactured but the backing also remains with the surface covering and is removed just prior to installation at the job site. The surface covering is secured at its perimeter only before the stresses therein are relieved.
Evans U.S. Pat. No. 4,159,219 teaches a method to produce an unbacked tension flooring by the specific design of two or more thermoplastic layers constructed such that when rolled, the outward facing layer elongates and the inward facing layer is compressed. Upon unrolling and placing flat, the elongated layer overcomes the compressed layer and thus a length greater than the original length before roll-up is generated. This elongation is defined herein as "roll-up growth". On securing the surface covering only at its periphery shortly after unrolling, the tendency of the surface covering to return to its original dimension, i.e. its elastic memory, creates a self-induced tension therein.
Greiner, Jr. et. al. U.S. Pat. No. 4,135,675 shows a paper carrier stripping method and apparatus which prevents uncontrolled tension from the necessary procedure of removing a strippable carrier from the structure before placing into a roll upon a windup stand.
Installation of these elongated tension floors by attachment at their periphery has produced one of the most reliable installation methods to accommodate fluctuating dimensional changes of unstable wood subfloors in today's environment. However, such tension floors are deficient in that the tension required to elongate the surface covering sufficiently to accommodate the dimensional change of wooden subfloors may be excessive. Further, the elongation of the surface covering is only in one direction.
Eckert et. al. U.S. Pat. No. 4,654,244 entitled "Loose-Lay and Adhered Surface Coverings" teaches the in-situ modification of reinforcing layers to form a surface covering capable of accommodating the movement of very unstable subfloors such as particle-board. One requirement of loose-lay flooring is that it must lay flat upon the subfloor and not curl or dome after installation. These loose-laid structures were balanced to provide lay-flat in-service characteristics.
A surface covering is balanced when the reinforcing layer is at the approximate neutral bending plane. The neutral bending plane is an imaginary plane within the surface covering above which the material is under tension and below which the material is under compression when the ends of the surface covering are subjected to a downward bending force.
Hensel U.S. Pat. No. 3,821,059 discloses another loose-lay surface covering. The reinforcing layer has a plurality of rigid elements separated by a resilient and compliant matrix.
But in spite of what was known, product and process deficiencies existed and improved performance was desirable in terms of rolling load resistance and cut or puncture expansion. In loose-lay floors, the reinforcing layer dominated the surface covering such that the flooring could not adjust to subfloor movement, resulting in buckling and other deformations. A need existed to eliminate the need for a strippable carrier and special apparatus to control pre-stressing of a self-induced tension product.
Prior to the present invention, it was not known that a flooring material could serve both loose-lay and tension floor applications. It was believed that for a tension floor to perform successfully the elongated length of the surface covering when installed must be greater than its relaxed length by at least as much as the subfloor on which it is installed may shrink due to environmental changes such as humid summer to dry winter seasonal changes. However, the magnitude of such a change in surface covering length would be unacceptable in a loose-lay floor since such shrinkage would pull the loose-lay surface covering noticeably away from the walls.